@mixin absolute($top: 0, $right: 0, $bottom: 0, $left: 0) {
  position: absolute;
  @if $top!=none {
    top: $top;
  }
  @if $left!=none {
    left: $left;
  }
  @if $right!=none {
    right: $right;
  }
  @if $bottom!=none {
    bottom: $bottom;
  }
}

@mixin fixed($top: 0, $right: 0, $bottom: 0, $left: 0) {
  position: fixed;
  @if $top!=none {
    top: $top;
  }
  @if $left!=none {
    left: $left;
  }
  @if $right!=none {
    right: $right;
  }
  @if $bottom!=none {
    bottom: $bottom;
  }
}
